In the manufacture of next generation integrated circuits, the fabrication of gate electrodes for complementary metal-oxide-semiconductor (CMOS) transistors has advanced to replace silicon dioxide and polysilicon with high-k dielectric materials and metal. A replacement metal gate process is often used to form the gate electrode. A typical replacement metal gate process begins by forming a high-k dielectric material and a sacrificial gate between a pair of spacers on a semiconductor substrate. After further processing steps, such as an annealing process, the sacrificial gate is removed and the resulting trench is filled with one or more metal layers. The metal layers can include workfunction metals as well as polysilicon electrode layers. This type of MOS transistor is often referred to as a high-k/metal gate transistor.
It has been shown that the reliability of the high-k gate dielectric layer tends to degrade over time. This is at least partially due to a high concentration of “dangling bonds” on the dielectric material, which serve as reactive sites and eventually lead to breakdown of the gate dielectric and failure of the MOS transistor. The dangling bonds therefore serve to decrease the performance, reliability, and lifetime of the transistor. Accordingly, improved methods of forming high-k/metal gate transistors are needed that can address the issue of dangling bonds in order to improve reliability in the high-k gate dielectric layer, thereby improving transistor performance and extending the life of the transistor.